Re: [PATCH] x86_64: Fix asm constraints in feraiseexcept (bug 30305)

[Noah Goldstein <goldstein.w.n@gmail.com>]

On Mon, Apr 3, 2023 at 10:43 AM Florian Weimer via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
> The divss instruction clobbers its first argument, and the constraints
> need to reflect that.  Fortunately, with GCC 12, generated code does
> not actually change, so there is no externally visible bug.
>
> Tested on x86_64-linux-gnu.
>
> Suggested-by: Jakub Jelinek <jakub@redhat.com>
>
> ---
>  sysdeps/x86_64/fpu/fraiseexcpt.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/sysdeps/x86_64/fpu/fraiseexcpt.c b/sysdeps/x86_64/fpu/fraiseexcpt.c
> index 924eed96a9..e7430a4158 100644
> --- a/sysdeps/x86_64/fpu/fraiseexcpt.c
> +++ b/sysdeps/x86_64/fpu/fraiseexcpt.c
> @@ -33,7 +33,7 @@ __feraiseexcept (int excepts)
>        /* One example of an invalid operation is 0.0 / 0.0.  */
>        float f = 0.0;
>
> -      __asm__ __volatile__ ("divss %0, %0 " : : "x" (f));
> +      __asm__ __volatile__ ("divss %0, %0 " : "+x" (f));
>        (void) &f;
>      }
>
> @@ -43,7 +43,7 @@ __feraiseexcept (int excepts)
>        float f = 1.0;
>        float g = 0.0;
>
> -      __asm__ __volatile__ ("divss %1, %0" : : "x" (f), "x" (g));
> +      __asm__ __volatile__ ("divss %1, %0" : "+x" (f) : "x" (g));
>        (void) &f;
>      }
>
>
> base-commit: ac2a14343e81098c196cef5d67b52e440c05c230
>

LGTM.

Reviewed-by: Noah Goldstein <goldstein.w.n@gmail.com